Can't see where or how you have the tank. Have you considered cutting the "motor box" to shorten the nose?
Also, maybe get rid of the universal mount and get a standard beam mount, if you can find some, that would let you move teh engine back a little more.
http://www.gravesrc.com/sigem001-sig...d-eng-mnt.html
http://www.gravesrc.com/han2033-hang...cap-12-15.html

Yes, you'd have to remount and/or shorten the cowl.
Just a couple of ways I would tackle that problem in order to use that engine.
I would rather lose 1/4" or so of the nose instead of adding 3-1/2 ounces of lead.